Pasta-Shaped Radio Waves Do The Twist

Radio waves normally propogate through the air in a pattern similar to waves rippling toward. But researchers have found a way to twisting radio waves into a spiral shape, which could them to cram more data into the signal. Not only that, but understanding the characteristics of these waves could shed light on powerful phenomena in space.

Bo Thide of the Swedish Institute of Space Physics in Uppsala and Fabrizio Tamburini of the University of Padua led a team that found a way to transmit radio waves in a helical, twisted pattern. Further, they did it in a real-world environment and at frequencies commonly used by Wi-Fi networks. The results appeared in The New Journal of Physics.

Tamburini told Discovery News that twisting radio waves was pioneered back in the 1970s. Researchers have also produced twisted laser light in the visible range. What he and Thide have done, though, is show that it’s possible to generate and receive such waves outdoors and pick them up outside of a laboratory. Tamburini and Thide managed to send the signal 442 meters (about 1,450 feet) across a stretch of water between the Piazza San Marco and San Giorgio Maggiore.

Better yet, transmitting such waves this way doesn’t require radical new technology. Part of the apparatus was an ordinary satellite dish antenna. “We bought it on eBay,” Tamburini said. A cut was made in one side to get it into a helical shape. To detect the altered shape of the radio signal, though, requires an additional antenna.

Twisting the radio waves in this way offers one more dimension in which to divide a signal. Currently, a radio signal can be split up so that many users can transmit on the same frequency. The signal can be divided into time slots, frequency slots, or each piece of information can be tagged so that the receiver only strings together a certain signal with all the others coming in as noise. Modern wireless computers and mobile phones combine all three methods.

A spiral-shaped radio wave offers yet another way to divide the signal. Using two or more antennas one could look at where along the spiral your message is, just as in code-divided signals a cell phone builds your voice from the pieces tagged with the right bits. Given that radio spectrum is in limited supply and more people are going wireless, it’s a technology that could save phone carriers a lot of money. (Tamburini said he has filed for patents on some parts of his idea).

Besides boosting bandwidth, though, twisted waves can show how a black hole or other really massive object spins. When black holes rotate, they drag space-time with them, and their mass is so great they bend it. Radio waves usually move in straight lines; the twisted shape can tell scientists a lot about how the black hole bends space itself.